Background: Platelets play a key role in the pathophysiology of thrombosis. Among the multiple mediators of platelet activation, adenosine diphosphate (ADP) plays a pivotal role. Genetic polymorphisms of the P2Y12 ADP receptor have been described which may influence the activation of this receptor by ADP or the response of patients to platelet inhibitors. Patients and Method: The present study was conducted on 40 patients diagnosed with acute coronary syndrome and 40 sex and aged matched healthy volunteers. Platelet aggregation was assessed (before and after clopidogrel administration) and Genotyping of the T744C polymorphism of the P2Y12 receptor gene was carried out using the PCR-RFLP method. Results: Platelet aggregation of the patients before clopidogrel administration had a range of 54 – 183 and had a range of 4 – 113 after the administration of Clopidogrel. 72.5% of the patients had a wild allele (TT) while 27.5% had a C allele (heterozygous CT, homozygous CC). On the other hand 97.5% of controls had wild allele (TT) while 2.5% had a C allele (heterozygous CT, homozygous CC). Conclusion: Our study found an association between the T744C polymorphism of the P2Y12 ADP receptor gene and platelet reactivity. Carrying C allele at this position is associated with an increased platelet activation response to ADP.